Human inflammatory bowel diseases (IBD's), including Crohn's disease and ulcerative colitis, are life-long, potentially debilitating intestina disorders thought to be due to overly-aggressive immune responses to normal bacteria that typically colonize the intestines. Current treatments focus on suppressing a person's immune system, which can lead to complications such as cancer and infections. The overall goal of this research is to better understand how bacteria contribute to the development of IBD's so that new medications can be developed that specifically target the intestinal microbes with minimal risk to the person. Recent data from animal models of IBD's suggest that inflammation causes intestinal bacteria to increase expression of small heat shock proteins, which in turn attenuate host inflammation. Whether anti-inflammatory properties of these heat shock proteins are also observed in other bacterial stress response systems is unknown and is the subject of these studies. Identifying and understanding the bacterial stress response systems that have anti- inflammatory properties could lead to the development of novel agents to treat IBD's by targeting master regulators of multiple bacterial stress response pathways. Preliminary data suggest that non-pathogenic E. coli in the colon also upregulate expression of acid resistance genes, gadA and gadB, during colitis and that these genes inhibit movement of the bacteria into intestinal tissues and prevent killing of E. coli by macrophages. The proposed studies aim to 1) Determine the effects of E. coli gadAB expression on the development of experimental IBD's, 2) Identify mechanisms by which E. coli gadAB expression inhibits movement of bacteria across intestinal epithelial cells, and 3) Study how E. coli GadAB promote bacterial survival within, and antigen processing by, macrophages. Interleukin-10 knockout mice, which develop spontaneous colitis when colonized by certain bacteria, will be selectively colonized with genetically altered non-pathogenic E. coli strains. In vitro studies of E. coli-infected T84 intestinal epithelial cell monolayers and bone-marrow derived macrophages will help determine mechanisms by which E. coli GadAB affects bacterial translocation and immune system activation. It is anticipated that completion of the proposed studies will: 1) identify novel functions of E. coli GadAB, 2) determine the anti-inflammatory potential of E. coli GadAB in experimental IBD's, 3) increase understanding of how IBD's develop, and 4) lead to future studies of manipulating bacterial stress responses for therapeutic purposes.